In recent years, markup languages, such as XML (Extensible Markup Language), have been used as document data processed by a computer. The XML can make it easy to share a structured document and structured data between different information systems through the Internet particularly, and thus has been increasingly used by computers (e. g., refer to Japanese Laid-open Patent Publication No. 05-101053). Hierarchically structured document data described based on the XML is hereinafter described as XML data.
As for techniques related to the XML data, a technique is known in which even if an author freely edits a document without any editorial constraint, the past document can be restored (e.g., refer to Japanese Laid-open Patent Publication No. 09-171510).
Conventionally, new XML data may be produced by taking specific data from a plurality of pieces of XML data and combining them for utilizing existing XML data. In combining the data, a user oneself needs to input a complicated query (Xquery) into a computer, so that a problem arises in that it is a heavy burden for the user to use the query.